The present invention is in an all-ceramic drill bit having a groove for shavings.
When drilling with HSS (high speed steel) and HM (hard metal) tools, an increase in the machining performance is possible only to a limited degree. The machine tool usually fails because the elevated-temperature hardness has been exceeded if the cutting speed is increased further. Such limitations result in longer manufacturing times for the corresponding operations and, consequently, a higher cost share during tool manufacture. Moreover, these tools require that a cooling lubricant be constantly supplied during use. However, the disposal of the used lubricants increasingly creates problems at the present time.
It has been found that a significant increase in performance may be obtained if the tool is formed or constructed of other materials. Because of the characteristic values of the materials and the positive development in the lathing and milling area, ceramic materials are desirable. Ceramic materials have a very high elevated-temperature hardness and wear resistance and thus promise significant advantages for increasing cutting speed values. In addition to a decrease in processing times, further advantages of using ceramic drilling tools include a very high surface quality, low wear values, and dry processing resulting in both economic and ecological advantages.
However, when designing a tool from a particular material, the characteristics of that material must be taken into account in the geometric design of the tool. Because the toughness of a ceramic is significantly less than that of HSS and HM, the material must have the highest possible cross section. As a result of the high cutting values and the consequently large volume of metal removed, the cross section of the grooves for the shavings must be as large as possible. The polished section of the chisel edge must therefore be designed so that crushing of material due to cutting speeds tending towards zero in the center of the drill are largely avoided (occurrence of tensile stresses in the cutting material).
All-ceramic drilling tools or drill bits with HSS geometries are known, see a publication of Bohrmeister Guehring, Mit Keramik in die Vollen, Volume 25, NO. 37/92, pages 14 to 17. However, in the known all ceramic drilling tools or bits, the polished section has not been adapted to the special properties of the ceramic material. The tools fail particularly due to fracture and chipping resulting from an incorrect geometry of the cutting material.
It is an object of the invention to provide an improved all-ceramic drill bit with a groove for shavings of a construction such that the positive properties of the ceramic are associated with a tool geometry adapted to the special features of the material.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention .